This is a proposal to study the immunobiology of the major histocompatibility complex, particularly that of I-region gene products. Peptide antigens will be synthesized and the specificity of the T cell immune response to these will be determined. The effects of varying the immunogen and the MHC-type of the antigen-presenting cell will be determined. These studies will be useful in defining whether the MHC-gene products act as part of the antigen receptor complex; if so, determining their specificity and the relationship of that specificity to immune response (Ir) gene effects. In order to accomplish these studies, T cell hybridomas will be constructed and the specificity of their antigen dependent IL-2 production assayed. The fusion of two such hybridomas to look for complementation of MHC-and antigen-receptors, when their putative antigen/Ia interactions are fixed, will be attempted.